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Question #43672

Difficulty: 8/10 | 🟢 Free

The Question

Two distant, mutually incoherent point sources S1S_1 and S2S_2 emit linearly polarized light of wavelength λ=500 nm\lambda = 500\text{ nm}. The electric field vector of the emitted light from both sources makes an angle of 45∘45^\circ with the vertical. A telescope is used to observe these sources. The telescope has a rectangular aperture of width a=2.0×10−3 ma = 2.0 \times 10^{-3}\text{ m} (horizontal) and height b=5.0×10−3 mb = 5.0 \times 10^{-3}\text{ m} (vertical). A special mask is placed over the aperture: the left half (−a/2≤x≤0-a/2 \le x \le 0) is covered by an ideal linear polarizer with its transmission axis vertical, and the right half (0≤x≤a/20 \le x \le a/2) is covered by an ideal linear polarizer with its transmission axis horizontal. What is the minimum angular separation θmin\theta_{min} between the two sources along the horizontal direction such that they are just resolved according to the Rayleigh criterion?

Options

  • A.

    2.5×10−4 rad2.5 \times 10^{-4}\text{ rad}

  • B.

    5.0×10−4 rad5.0 \times 10^{-4}\text{ rad}

  • C.

    1.25×10−4 rad1.25 \times 10^{-4}\text{ rad}

  • D.

    1.0×10−3 rad1.0 \times 10^{-3}\text{ rad}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Photon Polarization and Selection|Phase Difference vs. Path Difference|Resolving Power Limits|Small Angle Approximation

Why This Question Is Tricky

Common Mistakes

Students incorrectly apply the standard scalar Rayleigh criterion (θ=λ/a\theta = \lambda/a) without accounting for the vector nature of light.

The lethal trap lies in failing to recognize that orthogonal polarization states (created by the split polarizer mask) do not interfere.

Consequently, the aperture does not act as a single coherent slit of width aa, but rather as two independent slits of width a/2a/2 whose intensity patterns superimpose.

This modifies the effective geometry of the diffracting wavefront, doubling the angular spread of the central maximum and degrading the resolving power to 2λ/a2\lambda/a.

This tests the deep conceptual understanding that interference requires parallel electric field components.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterAtoms - Class 12
ConceptPhoton Polarization and Selection
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree